A problem of automatic dish washing compositions that are currently used in the market is that they may cause poor glass appearance attributed to glass corrosion and may affect the decor of articles, e.g. discolouration, fading and dullness of colours. This is especially true when using high pH compositions and the problem may be particularly noticeable for articles with on-glaze decoration.
GB-A-2,205,851 discloses the use of alkali metal silicate material as an anti-stain agent and indicates that these silicates improve the corrosion protection of the composition.
EP-A-0,446,761 discloses the use of alkali metal silicate material to provide alkalinity and protection of hard surfaces, such as fine china glaze and pattern.
Stannum compounds have also been suggested in the art to overcome glass corrosion, but these compounds may have negative effects on stain removal.
There is a tendency in the automatic dishwashing market towards the use of (relatively) low pH, say lower than 11, cleaning compositions that produce a washing liquor with a lower pH, say lower than 11. Such compositions have e.g. been described in DE 1,302,394 and EP-A-0,414,197.
We have found that, even though less noticeable, glass corrosion and/or decor problems (especially articles with on-glaze decoration) may still occur when wash liquors of lower pH are used. Glass corrosion is glass dissolution and may e.g. lead to weight loss and occurence of iridescence, which are not consumer preferred. Decor care problems are the fading of colours on articles with decoration.
Glass corrosion and decor problems in particular occur in wash liquor that comprises one or more ingredients selected from builder, bleach, enzymes, sequestrants, anti-scaling agents and crystal-growth inhibitors.
The compounds that have been suggested in the art to overcome the above problems are not usually suitable to be included in low pH product and/or have low performance at low pH, especially in liquids. For example, incorporation of sodium silicate in a low pH aqueous product (say with a pH of lower than 11) may severly increase the viscosity, due to polymerisation of the silicate. Further, silicate material has the disadvantage that it increases the product pH and it is a hazardous ingredient that can be aggressive to skin and eyes, especially when in the metasilicate and disilicate forms. Furthermore, we have found that silicate may lead to iridescence of glass, giving it a coloured appearance when held to the light.
We have further found that detergent compositions in the art show tarnishing effects, e.g. on silver articles like cutlery.
It is therefore an object of the present invention to reduce glass corrosion and/or improve decor care and/or protect the glaze of soiled articles and/or reduce iridescence, in particular on glasses and/or plates, after washing with a low pH cleaning composition in automatic dish washing processes. It is a further object of the present invention to reduce tarnishing. It is preferred to overcome all these problems.
Further, we have found that silica inclusion in liquid and/or solid detergent compositions (e.g. powder or tablet) may lead to problems. Silica material is very fine and has a low bulk density in comparison to other typical detergent ingredients. Silica has been found to give setting in liquid products and it has been found to separate out as well as affecting powder flow which also has deleterious consequences for tablets, e.g. on powder flow properties and tablet strength. Further, silica may not be well-delivered to the wash liquor from the mechanical dish washing composition, leading to lower effectiveness in overcoming one or more of the above mentioned problems.
It has now surprisingly been found that the glass corrosion and/or the decor care and/or glaze protection of soiled articles and/or iridescence when washed with a cleaning composition in an automatic dish washing process at a low pH can be substantially improved if the composition comprises silica material. We have further surprisingly found that tarnishing may be reduced by using silica material. It is in particular surprising as silica is known as an inert ingredient.
It has now surprisingly been found that silica inclusion problems and/or silica delivery problems can be substantially improved if the silica material is included in detergent compositions in aggregated and preferably in granulated form.